The invention relates to electroluminescent diodes and more specifically to electroluminescent edge-emitting diodes having low internal absorption to generated light.
Luminescence from an electroluminescent diode is the emission of optical radiation--ultraviolet, visible, or infrared--that is a direct result of the energy released during electronic transitions within a semiconductor material. The luminescence arises from a two-step process in which electrons and holes are generated in concentrations greater than those statistically permitted at thermal equilibrium and then a significant fraction of these carriers recombine. Radiative recombination occurs when the energy of the recombining holes and electrons generates photons.
An electroluminescent edge-emitting diode is one in which the generated light is emitted from only one surface having partial directionality. In the past, electroluminescent edge-emitting diodes have been less efficient as a result of a large portion of the generated light being internally absorbed by the diode and never radiating from the emitting surface. When speaking of efficiency, we are concerned with the quantum efficiency of an electroluminescent diode, which simply is the ratio of photons produced to the number of electrons passing through the diode. The internal quantum efficiency is evaluated at the P-N junction whereas the external quantum efficiency is evaluated at the exterior of the diode. The external quantum efficiency is always less than the internal quantum efficiency as a result of optical losses that occur in extracting the emitted radiation from the diode, one cause of which is internal absorption. Thus, it would be most desirable in the field of electroluminescent edge-emitting diodes to have a diode in which the effect of internal absorption is maintained.